Binders are used in “green” ceramic processing to increase the overall mechanical strength before firing to ensure all parts make it to the sintering stage. Using a binder in a ceramic system prevents ceramic parts from breaking or falling apart during various methods of production until the pieces are ready to be fired. There are many varieties of ceramic binders, but effective ones must meet all the following standards:
Increase mechanical strength
Do not cause sticking of ceramic paste to processing equipment
Effectively burn out with low ash content upon firing
No interference with glazing
Types of Ceramic Binders
The ceramic industry uses dozens of different binders, but the majority can be categorized as either inorganic or organic.
Inorganic Binders
Inorganic binders are mineral based, often with silicate chemistry. These additives increase mechanical strength during extremely high temperature ceramic processing. Common materials are sodium silicate and bentonite. While relatively inexpensive, inorganic binders can require a higher amount of material leading to potential viscosity issues and ceramic defects during extrusion.
Organic Binders
Organic binders are all non-mineral based polymeric materials that work by forming hydrogen bonds with ceramic powder particles during the drying process. These binders are typically more expensive than inorganic, but they can often be used in smaller amounts and offer some benefits exclusive to organic materials during ceramic extrusion and processing.
The Ideal Ceramic Binder is METHOCEL™
METHOCEL™ is a product line by IFF featuring methylcellulose and hydroxypropyl methylcellulose powders. These powders are effective organic binders and processing aids during the production of high-performance ceramics. These polymers are water-soluble and unique to other organic binders due to a three-dimensional gel structure forming at high temperatures. This structure provides additional stability to the consolidated powder compact (green body) ceramic components during extrusion, when drying, and during the firing process. This METHOCEL™ structure during thermal gelation also prevents the binder from migrating and reduces the possibility of stress cracks and blisters during the sintering process.
Binder Migration Prevention
As ceramic bodies dry, many organic binders will migrate to the surface along with the evaporating water content. A “skin” can form because of this process that inhibits further drying, leading to issues upon firing. When fired, the uneven binder distribution can lead to surface defects such as stress cracks and grain growth as the material sinters into a solid-state.
METHOCEL™ binders remain fixed and do not migrate during the drying process due to the three-dimensional network formed during thermal gelation. This allows ceramic bodies that contain METHOCEL™ to fire more consistently without debinding and be less likely to show surface defects.
Using METHOCEL™ To Improve Ceramic Processes
METHOCEL™ can simplify ceramic manufacturing processes and improve efficiency. The thermal gelation characteristic described above improves more than just the green strength of ceramic bodies. When added as a binder, METHOCEL™ changes the ceramic mix from adhesive to cohesive at gelation temperatures.
The Effect of Thermal Gelation on Green Strength
The graph above illustrates the sharp increase in green strength using a torque rheometer to measure the viscosity of an alumina ceramic mixture containing METHOCEL™ A4M when held above thermal gelation temperatures.
Ceramic Mix in a Torque Rheometer
These images show a ceramic mix containing METHOCEL™ observed in a torque rheometer at temperatures above and below the thermal gelation point. When the ceramic mix is above the thermal gelation point, it does not stick and is able to separate cleanly from metal surfaces during ceramic processing. This characteristic is extremely helpful during injection molding and engineering fine ceramic extrusions.
METHOCEL™ Binder Variations
The dynamic viscosity, thermal gelation temperature, and gel firmness of a ceramic mix containing METHOCEL™ varies based on the grade and concentration used.
At varying concentration levels and temperatures, a significant increase in viscosity occurs due to thermal gelation. This increase makes it easy to create the right balance of properties for your particular ceramic application.
Other METHOCEL™ grades may be recommended based on your requirements.
Our specialists would be happy to assist you in finding the right grade of METHOCEL™ and getting you a sample. Click below to discuss your application with us.
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